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Available-for-sale securities (Details) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Available-for-sale securities [Line Items] |  |  |
Investments used to satisfy obligations under nonqualified benefit plans | $ 62,400,000 | $ 48,900,000 |
Net unrealized gain (loss) of investments used to satify obligations under nonqualified benefit plans | 13,500,000 | 5,200,000 | (1,100,000)
Available-for-sale securities: |  |  |
Available-for-sale securities [Abstract] |  |  |
Available-for-sale securities, amortized cost basis | 10,057,000 | 9,817,000 |
Available-for-sale securities, gross unrealized gains | 84,000 | 187,000 |
Available-for-sale securities, gross unrealized losses | (31,000) | (3,000) |
Available-for-sale securities | 10,110,000 | 10,001,000 |
Mortgage-backed securities |  |  |
Available-for-sale securities [Abstract] |  |  |
Available-for-sale securities, amortized cost basis | 8,151,000 | 8,054,000 |
Available-for-sale securities, gross unrealized gains | 69,000 | 144,000 |
Available-for-sale securities, gross unrealized losses | (27,000) | (3,000) |
Available-for-sale securities | 8,193,000 | 8,195,000 |
U.S. Treasury securities |  |  |
Available-for-sale securities [Abstract] |  |  |
Available-for-sale securities, amortized cost basis | 1,906,000 | 1,763,000 |
Available-for-sale securities, gross unrealized gains | 15,000 | 43,000 |
Available-for-sale securities, gross unrealized losses | (4,000) | 0 |
Available-for-sale securities | $ 1,917,000 | $ 1,806,000 |

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- Definition Investments used to satisfy obligations under unfunded, nonqualified benefit plans for executive officers and certain key management employees. + References No definition available. + Details
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- Definition Net unrealized gain (loss) of investments used to satify obligations under unfunded, nonqualified benefit plans for executive officers and certain key management employees. + References No definition available. + Details
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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 + Details
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- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 + Details
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- Definition Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 + Details
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